FoundationDB is used at Datadog as the metadata store for Husky, the storage and query engine powering a significant number of Datadog products, such as logs, network performance monitoring, and trace analytics.
I know there are multiple companies that use it. The question is not whether people put things into FDB. The question is whether anyone has checked to see if their junk was still there later. I don't consider large scale deployments to be proof of anything. When I worked on Gmail we were still finding data-loss bugs in either BigTable or Colossus regularly, even after those systems had been the largest datastores on the planet for many years.
1. https://www.datadoghq.com/blog/engineering/introducing-husky...
2. https://www.datadoghq.com/blog/engineering/husky-deep-dive/
3. https://www.youtube.com/watch?v=mNneCaZewTg
4. https://www.youtube.com/watch?v=1-zo9jqdRZU
I was involved with this project from the beginning and it would've taken significantly longer to deliver without FoundationDB.